1. Field of the Invention
The present invention relates to a method for detecting an abnormal electric-cell, and more particularly to a method for detecting an abnormal electric-cell in a battery system including a plurality of blocks serially connected together, wherein each of the plurality of blocks includes a plurality of cells serially connected together.
2. Description of the Related Art
A hybrid electric vehicle uses a battery system including a plurality of blocks serially connected together, wherein each of the plurality of blocks includes a plurality of cells serially connected together.
The following abnormal cell detecting methods are known in the art for use with the battery system as described above: a method for detecting a block which includes an abnormal cell by calculating an internal resistance for each block based on the relationship between the block voltage and the current for each block; and a method for detecting a block which includes an abnormal cell based on the difference in voltage between blocks.
However, in the former conventional method in which the internal resistance is calculated for each block based on the relationship between the block voltage and the current for each block, the influence of current hysteresis is considerable. Thus, there is a problem that it is difficult to calculate the internal resistance accurately.
The latter conventional method has a problem as follows. There may be a difference in temperature among a plurality of cells. Therefore, if a battery system is used for a long period of time, unevenness in capacitance among the cells occurs. Accordingly, a difference in voltage among blocks occurs. Thus, in the method for detecting a block which includes an abnormal cell based on the difference in voltage between blocks, there is a problem that it is difficult to distinguish a difference in voltage between the blocks because of the presence of the abnormal cell from a difference in voltage between the blocks because of the unevenness in capacitance.
If the discharge electric power and the charge electric power are calculated for each block in a method for detecting an abnormal cell, a cell in which a drop in electromotive force, a minor short, a short, etc., has occurred may be detected as an abnormal cell as well as a cell in which the internal resistance has increased.